In a radio communications system, in order for a UE (user equipment) to measure a downlink channel and obtain downlink CSI (channel state information), a base station needs to send an RS (reference signal) to the UE in a coverage area. For example, in a 3GPP (the 3rd generation partnership project) LTE (long term evolution) R (release) 10 protocol, the base station needs to send a non-zero-power CSI-RS (channel state information reference signal) to the UE in the coverage area so that the UE can measure the downlink channel. The base station may also send a zero-power CSI-RS to avoid interference onto the non-zero-power CSI-RS of a neighboring cell. In the existing LTE R10 protocol, the base station sends a non-zero-power CSI-RS and a zero-power CSI-RS to the UE on an RE (resource element). When the number of REs occupied by the non-zero-power CSI-RS and the zero-power CSI-RS increases, the number of REs for transmitting data symbols decreases, which leads to a low utilization efficiency of the REs.